I'd like to know if anyone is motivated by Chimezie's comment suggesting
that a FROM * and a FROM NAMED * be added to SPARQL to "provide an
unambiguous way to specify a dataset which corresponds to all the known
named graphs."
I'm wary of adding this for a couple of reasons:
1/ I can't imagine how such a construct would be defined such that it was
any different from the implementation-defined state which currently exists
when FROM and FROM NAMED are omitted. (And, therefore, the construct
doesn't seem to add anything new or newly interoperable to the
specification.)
2/ Existing implementations solve this problem within the current bounds
of SPARQL (see the IRC chat log cited for two examples)
If you have a strong feeling one way or the other, please let it be known
so that I can gauge whether the group has consensus (and either reply to
Chimezie or slot this item on our teleconference agenda for next week).
Lee
----- Forwarded by Lee Feigenbaum/Cambridge/IBM on 04/05/2007 03:16 AM
-----
"Chimezie Ogbuji" <ogbujic@ccf.org>
Sent by: public-rdf-dawg-comments-request@w3.org
04/04/2007 05:05 PM
Please respond to
ogbujic@ccf.org
To
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Subject
No way to specify an RDF dataset of all the known named graphs
This was discussed in #swig
(http://chatlogs.planetrdf.com/swig/2007-04-03.html#T20-38-01)
SPARQL currently does not provide an unambiguous way to specify a
dataset which corresponds to all the known named graphs. The only way
this can be done is to leave out FROM <..> and FROM NAMED <..>
directives in the prolog (and from the protocol, for SPARQL services).
The corresponding dataset in this case depends on the host application -
not very consistent. The only other alternative is to explicitly
enumerate the known universe in the prolog:
FROM NAMED G1
FROM NAMED G2
...
FROM NAMED GN
This is not practical for a dynamic dataset.
There is plenty of value in querying against the known universe
consistently especially for applications which make use of a dataset as
a named graph partition that can grow indefinitely. Consider XPath
2.0 / XQuery 1.0 which supports querying a collection of XML documents
without having to explicitly enumerate all the XML documents in the
collection.
This is a very useful 'database-wide' query pattern which is well
supported in document-management languages but not supported in SPARQL
without assuming the implementation will consistently supply the dataset
corresponding to all the known named graphs in persistence in the
absence of any dataset directives in the prolog or at the protocol
level.
Other than OWA or CWA issues, I don't see why an explicit syntax for
binding to such a dataset is not supported by SPARQL to provide a
consistent way for applications to dispatch these kinds of queries.
Such a syntax was suggested in the above conversation:
FROM NAMED *
[1] http://www.w3.org/TR/xquery-semantics/#sec_fn_doc_collection
--
Chimezie Ogbuji
Lead Systems Analyst
Thoracic and Cardiovascular Surgery
Cleveland Clinic Foundation
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ogbujic@ccf.org
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